1. Field of the Invention
The present invention relates generally to printing cylinders, and in particular, to a printing cylinder that is removably supported on a hydraulically expansible mandrel, whereby the cylinder can be damaged by forces exerted by the expanding mandrel.
2. Description of the Related Art
Printing rollers with removably supported printing cylinders are generally known. By way of example, one such printing roller is described in U.S. Pat. No. 4,381,709 which is fully incorporated herein by reference and made a part of this disclosure. As described in U.S. Pat. No. 4,381,709, an expandable sleeve located at each end of a printing mandrel radially expands as a result of application of hydraulic pressure to hold a printing cylinder in position relative to the mandrel. To remove the cylinder, the hydraulic pressure is removed and the cylinder is slidably removed from the mandrel.
Application of hydraulic pressure causes each sleeve to expand radially, with the maximum radial increase being at substantially the midpoint of each sleeve between its two axial ends. As the hydraulic pressure is increased, the maximum radius of the sleeve continues to increase, causing a circumferential and relatively concentrated interference fit between the sleeve and the cylinder, and a corresponding stress increase within the cylinder at the interference region. As the hydraulic pressure is changed, both the radial forces acting on the cylinder and the area over which the forces act undergo a change.
In prior art printing rollers, a steel cylinder was provided with a plurality of small holes to carry the ink. The holes were made by suitable machining processes, such as by knurling or the like. More recently, such cylinders have been made of lightweight, relatively thinwall steel construction to accommodate the addition of a coating suitable for printing applications. One of the coatings which is used is generally described as an "analox" coating which is a relatively smooth, but delicate ceramic material which is layered on the outer surface of the steel cylinder. The analox coating is generally applied directly to the outer surface of the cylinder and is highly polished, then ground and laser etched to form a multiplicity of small ink carrying holes. When the cylinder surface is inked and the excess ink is wiped off the cylinder, the ink carried in the small holes is used to provide the precision printing. Other coating materials are contemplated.
It has been found that the substantial hydraulic forces exerted on the cylinder by the hydraulically operable mandrel can cause cylinder stresses that can undesirably deform the cylinder and crack the relatively brittle outer analox coating on the cylinder.
U.S. Pat. Nos. 4,407,199, 4,386,566 and 4,383,483 to Moss disclose removably supported printing cylinders having attached thick end reinforcing rings grippable by mandrel mounted expansion sleeves. Radial forces from the expansion sleeves are received by the thick reinforcing rings. U.S. Pat. No. 4,794,858 to Katz discloses a pneumatic release mandrel for the support of a printing cylinder. U.S. Pat. No. 5,507,228 to Schultz discloses a removably supported printing cylinder without reinforcing rings. The patent shows a single full length expansion sleeve having grooves cut into each end to facilitate expansion of the sleeve region between the grooves. The sleeve is sealingly attached to the mandrel. U.S. Pat. Nos. 4,934,266 to Fantoni also shows a single full length expansion sleeve as an integral part of a mandrel.
I have invented a printing cylinder assembly which incorporates a coated relatively lightweight printing cylinder supported on a mandrel in a manner which avoids the development of damaging forces to the outer surface of the cylinder.